Principles & Guidelines

There are 12 guidelines, comprised of 62 success criterion, in the WCAG 2.0 which are organized by the following 4 principles that lay the foundation necessary for anyone to access and use Web content. Anyone who wants to use the Web must have content that is:

1. Perceivable - Information and user interface components must be presentable to users in ways they can perceive. This means that users must be able to perceive the information being presented (it can't be invisible to all of their senses)

   • Guideline 1.1: Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language
     • Success Criterion 1.1.1: Implement text alternatives on all images and other non-text content
   • Guideline 1.2 Time-based Media: Provide alternatives for time-based media
     • Success Criterion 1.2.1: Audio-only and Video-only (Prerecorded): For prerecorded audio-only and prerecorded video-only media, the following are true, except when the audio or video is a media alternative for text and is clearly labeled as such:
       • Prerecorded Audio-only: An alternative for time-based media is provided that presents equivalent information for prerecorded audio-only content.
       • Prerecorded Video-only: Either an alternative for time-based media or an audio track is provided that presents equivalent information for prerecorded video-only content.
     • Success Criterion 1.2.2: Captions (Prerecorded): Captions are provided for all prerecorded audio content in synchronized media, except when the media is a media alternative for text and is clearly labeled as such
     • Success Criterion 1.2.3: Audio Description or Media Alternative (Prerecorded): An alternative for time-based media or audio description of the prerecorded video content is provided for synchronized media, except when the media is a media alternative for text and is clearly labeled as such
     • Success Criterion 1.2.4 Captions (Live): Captions are provided for all live audio content in synchronized media. (Level AA)
     • Success Criterion 1.2.5 Audio Description (Prerecorded): Audio description is provided for all prerecorded video content in synchronized media. (Level AA)
   • Guideline 1.3 Adaptable: Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
     • Success Criterion 1.3.1 Info and Relationships: Information, structure, and relationships conveyed through presentation can be programmatically determined or are available in text.
     • Success Criterion 1.3.2 Meaningful Sequence: When the sequence in which content is presented affects its meaning, a correct reading sequence can be programmatically determined.
     • Success Criterion 1.3.3 Sensory Characteristics: Instructions provided for understanding and operating content do not rely solely on sensory characteristics of components such as shape, size, visual location, orientation, or sound.
   • Guideline 1.4: Distinguishable: Make it easier for users to see and hear content including separating foreground from background
     • Success Criterion 1.4.1: Use of Color: Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element.
     • Success Criterion 1.4.2: Audio Control: If any audio on a Web page plays automatically for more than 3 seconds, either a mechanism is available to pause or stop the audio, or a mechanism is available to control audio volume independently from the overall system volume level.
     • Success Criterion 1.4.3 Contrast (Minimum): The visual presentation of text and images of text has a contrast ratio of at least 4.5:1, except for the following: (Level AA)
       • Large Text: Large-scale text and images of large-scale text have a contrast ratio of at least 3:1;
       • Incidental: Text or images of text that are part of an inactive user interface component, that are pure decoration, that are not visible to anyone, or that are part of a picture that contains significant other visual content, have no contrast requirement.
       • Logotypes: Text that is part of a logo or brand name has no minimum contrast requirement.
     • Success Criterion 1.4.4 Resize text: Except for captions and images of text, text can be resized without assistive technology up to 200 percent without loss of content or functionality. (Level AA)
     • Success Criterion 1.4.5 Images of Text: If the technologies being used can achieve the visual presentation, text is used to convey information rather than images of text except for the following: (Level AA)
       • Customizable: The image of text can be visually customized to the user's requirements;
       • Essential: A particular presentation of text is essential to the information being conveyed.
       • Note: Logotypes (text that is part of a logo or brand name) are considered essential.

2. Operable - User interface components and navigation must be operable. This means that users must be able to operate the interface (the interface cannot require interaction that a user cannot perform)

   • Guideline 2.1 Keyboard Accessible: Make all functionality available from a keyboard
     • Success Criterion 2.1.1 Keyboard: All functionality of the content is operable through a keyboard interface without requiring specific timings for individual keystrokes, except where the underlying function requires input that depends on the path of the user's movement and not just the endpoints.
       • Note 1: This exception relates to the underlying function, not the input technique. For example, if using handwriting to enter text, the input technique (handwriting) requires path-dependent input but the underlying function (text input) does not.
       • Note 2: This does not forbid and should not discourage providing mouse input or other input methods in addition to keyboard operation.
     • Success Criterion 2.1.2 No Keyboard Trap: If keyboard focus can be moved to a component of the page using a keyboard interface, then focus can be moved away from that component using only a keyboard interface, and, if it requires more than unmodified arrow or tab keys or other standard exit methods, the user is advised of the method for moving focus away.
       • Note: Since any content that does not meet this success criterion can interfere with a user's ability to use the whole page, all content on the Web page (whether it is used to meet other success criteria or not) must meet this success criterion. See Conformance Requirement 5: Non-Interference.
   • Guideline 2.2 Enough Time: Provide users enough time to read and use content.
     • Success Criterion 2.2.1 Timing Adjustable: For each time limit that is set by the content, at least one of the following is true:
       • Turn off: The user is allowed to turn off the time limit before encountering it; or
       • Adjust: The user is allowed to adjust the time limit before encountering it over a wide range that is at least ten times the length of the default setting; or
       • Extend: The user is warned before time expires and given at least 20 seconds to extend the time limit with a simple action (for example, "press the space bar"), and the user is allowed to extend the time limit at least ten times; or
       • Real-time Exception: The time limit is a required part of a real-time event (for example, an auction), and no alternative to the time limit is possible; or
       • Essential Exception: The time limit is essential and extending it would invalidate the activity; or
       • 20 Hour Exception: The time limit is longer than 20 hours.
       • Note: This success criterion helps ensure that users can complete tasks without unexpected changes in content or context that are a result of a time limit. This success criterion should be considered in conjunction with Success Criterion 3.2.1, which puts limits on changes of content or context as a result of user action.
     • Success Criterion 2.2.2 Pause, Stop, Hide: For moving, blinking, scrolling, or auto-updating information, all of the following are true:
       • Moving, blinking, scrolling: For any moving, blinking or scrolling information that (1) starts automatically, (2) lasts more than five seconds, and (3) is presented in parallel with other content, there is a mechanism for the user to pause, stop, or hide it unless the movement, blinking, or scrolling is part of an activity where it is essential; and
       • Auto-updating: For any auto-updating information that (1) starts automatically and (2) is presented in parallel with other content, there is a mechanism for the user to pause, stop, or hide it or to control the frequency of the update unless the auto-updating is part of an activity where it is essential.
   • Guideline 2.3: Do not design content in a way that is known to cause seizures
     • Success Criterion 2.3.1 Three Flashes or Below Threshold: Web pages do not contain anything that flashes more than three times in any one second period, or the flash is below the general flash and red flash thresholds. 
   • Guideline 2.4: Provide ways to help users navigate, find content, and determine where they are
     • ​Success Criterion 2.4.1 Bypass Blocks: A mechanism is available to bypass blocks of content that are repeated on multiple Web pages.
     • Success Criterion 2.4.2 Page Titled: Web pages have titles that describe topic or purpose.
     • Success Criterion 2.4.3 Focus Order: If a Web page can be navigated sequentially and the navigation sequences affect meaning or operation, focusable components receive focus in an order that preserves meaning and operability.
     • Success Criterion 2.4.4 Link Purpose (In Context): The purpose of each link can be determined from the link text alone or from the link text together with its programmatically determined link context, except where the purpose of the link would be ambiguous to users in general.
     • Success Criterion 2.4.5 Multiple Ways: More than one way is available to locate a Web page within a set of Web pagesexcept where the Web Page is the result of, or a step in, a process. (Level AA)
     • Success Criterion 2.4.6 Headings and Labels: Headings and labels describe topic or purpose. (Level AA)
     • Success Criterion 2.4.7 Focus Visible: Any keyboard operable user interface has a mode of operation where the keyboard focus indicator is visible. (Level AA)

3. Understandable - Information and the operation of user interface must be understandable. This means that users must be able to understand the information as well as the operation of the user interface (the content or operation cannot be beyond their understanding)

   • Guideline 3.1 Readable: Make text content readable and understandable.
     • Success Criterion 3.1.1 Language of Page: The default human language of each Web page can be programmatically determined.
     • Success Criterion 3.1.2 Language of Parts: The human language of each passage or phrase in the content can be programmatically determined except for proper names, technical terms, words of indeterminate language, and words or phrases that have become part of the vernacular of the immediately surrounding text. (Level AA)
   • Guideline 3.2 Predictable: Make Web pages appear and operate in predictable ways.
     • Success Criterion 3.2.1 On Focus: When any component receives focus, it does not initiate a change of context.
     • Success Criterion 3.2.2 On Input: Changing the setting of any user interface component does not automatically cause a change of context unless the user has been advised of the behavior before using the component.
     • Success Criterion 3.2.3 Consistent Navigation: Navigational mechanisms that are repeated on multiple Web pages within a set of Web pages occur in the same relative order each time they are repeated, unless a change is initiated by the user. (Level AA)
     • Success Criterion 3.2.4 Consistent Identification: Components that have the same functionality within a set of Web pages are identified consistently. (Level AA)
   • ​Guideline 3.3 Input Assistance: Help users avoid and correct mistakes.
     • Success Criterion 3.3.1 Error Identification: If an input error is automatically detected, the item that is in error is identified and the error is described to the user in text.
     • Success Criterion 3.3.2 Labels or Instructions: Labels or instructions are provided when content requires user input. 
     • Success Criterion 3.3.3 Error Suggestion: If an input error is automatically detected and suggestions for correction are known, then the suggestions are provided to the user, unless it would jeopardize the security or purpose of the content. (Level AA)
     • Success Criterion 3.3.4 Error Prevention (Legal, Financial, Data): For Web pages that cause legal commitments or financial transactions for the user to occur, that modify or delete user-controllable data in data storage systems, or that submit user test responses, at least one of the following is true: (Level AA)
       1. ​Reversible: Submissions are reversible.
       2. Checked: Data entered by the user is checked for input errors and the user is provided an opportunity to correct them.
       3. Confirmed: A mechanism is available for reviewing, confirming, and correcting information before finalizing the submission.

4. Robust - Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies. This means that users must be able to access the content as technologies advance (as technologies and user agents evolve, the content should remain accessible)

   • Guideline 4.1 Compatible: Maximize compatibility with current and future user agents, including assistive technologies.
     • Success Criterion 4.1.1 Parsing: In content implemented using markup languages, elements have complete start and end tags, elements are nested according to their specifications, elements do not contain duplicate attributes, and any IDs are unique, except where the specifications allow these features. (Note: Start and end tags that are missing a critical character in their formation, such as a closing angle bracket or a mismatched attribute value quotation mark are not complete.)
     • Success Criterion 4.1.2 Name, Role, Value: For all user interface components (including but not limited to: form elements, links and components generated by scripts), the name and role can be programmatically determined; states, properties, and values that can be set by the user can be programmatically set; and notification of changes to these items is available to user agents, including assistive technologies. (Note: This success criterion is primarily for Web authors who develop or script their own user interface components. For example, standard HTML controls already meet this success criterion when used according to specification.)

See the How to Comply webpage to find out what you can do to ensure that you are creating website content that is accessible according to these guidelines.